Python: [WIP] Create/Get Agent API

[dmytrostruk]

Motivation and Context

This PR contains an implementation for Option 1 from this ADR for Azure AI V2 chat client.

Remaining items:

• Unit & integration tests
• Samples

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the Contribution Guidelines
• All unit tests pass, and I have added new tests where possible
• Is this a breaking change? If yes, add "[BREAKING]" prefix to the title of the PR.

[moonbox3]

Python Test Coverage Report •

File	Stmts	Miss	Cover	Missing
packages/azure-ai/agent_framework_azure_ai
_client.py	364	143	60%	240–243, 248, 251–254, 259, 262–263, 266, 273, 374, 431, 468, 470, 475, 477–478, 480–488, 490, 528, 551, 593–594, 601, 603–613, 615, 621, 626, 654–655, 660–661, 663–664, 670–671, 673, 703–712, 759, 775–777, 779–796, 804–807, 810–811, 814–821, 826–827, 833–835, 838–839, 841, 853, 855–856, 858–859, 861–862, 864–872, 874, 902, 904–907, 909, 915, 921, 925, 940, 943–944, 946
TOTAL	17048	2743	83%

Python Unit Test Overview

Tests	Skipped	Failures	Errors	Time
2571	149 💤	0 ❌	0 🔥	59.697s ⏱️